Range synchronized flash photographic apparatus and method for achieving optimum flash exposure

ABSTRACT

An image recording apparatus and method employing a diaphragm shutter having a time variable exposure aperture with flash firing, following actuation of the shutter, after a time interval dependent on subject range. The functional relationship between the time interval and subject range establishes a parametric relationship between the brightness of the subject due to its flash illumination and the scan time of the diaphragm shutter. The inverse of this parametric relationship constitutes the timewise variation in the exposure aperture area of the shutter. Consequently, whenever the subject is within a predetermined maximum distance from the camera, dependent upon the maximum aperture area attainable by the shutter, the instantaneous product of subject brightness and aperture area will be a constant with the result that proper exposure of the photographic film is achieved independent of the subject range.

BACKGROUND OF THE INVENTION

This invention relates to a method of and apparatus for recording animage as by photography of a subject under flash illumination withoptimum exposure independent of the range of the subject.

In the photographic art, exposure systems employing a diaphragm orscanning shutter having an exposure aperture area that varies with timeduring the exposure interval are known. Representative patents showingscanning shutters are U.S. Pat. No. 3,762,299; U.S. Pat. No. 3,972,058and U.S. Pat. No. 4,047,190. In the above patents, a scanning shutter isdescribed which includes a pair of counter reciprocal blades each havinga primary aperture that traverses the optical axis of the camera duringthe exposure interval. These primary apertures are shaped so that uponoverlying one another during counter movement of the blades, theexposure aperture value, defined in part by one primary aperture and inpart by the other primary aperture, increases from zero to a maximumvalue in a preselected period of time.

In these arrangements, exposure control is exerted by a summing orintegrator circuit whose resistance is constituted by a photocelllocated behind a photocell aperture formed by secondary apertures in theblades. Like the exposure aperture value, the photocell aperture valueis also designed to change with time, such change being synchronizedwith the change in the exposure aperture value so as to provide properexposure control over a wide range of conditions. The photocell aperturevalue which controls the scene light emitted to the photocell openscoincident with or in slightly leading arrangement to passage of firstlight through the exposure aperture, and when the integrator reaches agiven level, a trigger circuit is fired a reverse the scan movements ofthe blades, which are rapidly returned to their initial positionblocking passage of scene light to the photosensitive recording medium,i.e., the film.

As indicated in the above-noted patents, the diaphragm shutter systemand its exposure control arrangements are designed for operation of thecameras in either an ambient or flash mode of operation, and the shapeof the primary and secondary blade apertures are important to obtainingproper exposure in both modes. In these arrangements, for the flash modeof operation, the scanning blades are stopped at an aperture valuepreselected in accordance with the position of the camera lens andhence, are responsive to subject range. Consequently, while the aperturevalues are varied prior to flash firing, a preselected fixed aperture isactually provided during the flash pulse.

Scanning shutters which utilize varying apertures during the flash pulseare also known as shown by U.S. Pat. No. 3,570,381 and U.S. Pat. No.4,020,497. In these patents, a flash fire switch is adjusted inaccordance with lens focusing so that the flash will coincide with arange of aperture values; this range of aperture values being selectedautomatically in accordance with lens focusing and hence subject range.While these dynamic flash systems will in many instances providesatisfactory flash exposure, it should be recognized that they aredependent upon a variable switch arrangement which is subject tomechanical position errors. Additionally, in U.S. Pat. No. 4,047,191, anincandescent flash is ignited coincident with or just prior to openingof a scanning shutter with the flash illumination envelope superimposedin a leading arrangement on the aperture opening curve so as to provideincreasing illumination intensity in slightly leading relation to theincreasing aperture values.

One attempt to further improve flash exposure is suggested in U.S. Pat.No. 3,794,422 wherein the transmissivity of an electro-optical shutteris varied as a function of the speed of light so as to provide uniformexposure of all subjects within the flash range. In this arrangement,the flash is fired as the transmissivity of the shutter is varied from ablocking condition such that the transmissivity will be relatively lowwhen the flash is fired but rapidly increases to a maximum. If a subjectis relatively close to the camera, it will appear to be relativelybrightly illuminated, however, the light reflected from that closesubject will be received by the shutter when its transmissivity isrelatively low. Under such condition, the shutter will relativelystrongly attenuate this reflected light such that only a predeterminedamount will pass. However, where the subject is relatively distant, thesame amount of light will pass even though the subject will appearconsiderably less bright, because by the time the light is reflectedfrom the distant subject the shutter transmissivity will have increasedto a level functionally related to this dimmer light. Although thejust-described arrangement is at least theoretically possible, it can beseen that the requirements for such a electro-optical shutter presentssevere complications as to size, weight and expense both in terms of theshutter itself as well as the modulator required to produce the requiredchange in transmissivity. Additionally, since the shutter functions inthe order of the speed of light, the precision required for the flashdevice and its firing time are also unduly burdensome.

It is, therefore, an object of the present invention to provide a newand improved method of and apparatus for photographing a subject underflash illumination to achieve an optimum exposure with such transientillumination.

Another object is to provide a method of and apparatus for achievingoptimum exposure under combined transient and steady state illumination.

SUMMARY OF THE INVENTION

Briefly, in the inventive arrangement, flash illumination of a subjectto be photographed, using a scanning shutter having a time-variableexposure aperture area, is accomplished by driving the shutter at aselected scan rate and producing a flash or pulse of illumination at theend of a time interval, measured from actuation of the shutter (i.e.,time of first light), dependent on both the range of the subject and theshutter scan rate. The functional relationship between the time intervaland subject range establishes a parametric relationship between thebrightness of the subject due to its flash illumination and the scantime of the shutter. The inverse of this parametric relationshipconstitutes the timewise variation in the exposure aperture area of theshutter. For a given flash output, whenever the subject is within apredetermined maximum distance from the camera (dependent on the maximumaperture area attainable by the shutter) the instantaneous product ofsubject brightness and aperture area will be a constant, resulting inproper exposure of the film independently of subject range. In thepreferred embodiments, the timed interval is determined by a rangefinderemploying sonic detection.

Briefly, the method includes the steps of determining a timed intervalproportionally related to subject range, exposing a recording mediumthrough increasing aperture values whose rate of increasing area iscorrelated to the interval-range proportion, and providing a pulse ofillumination, following initiation of said exposing step, after a periodrelated to said timed interval so that said illumination pulse issynchronized with an aperture value, or small range of aperture values,selected in accordance with subject range to provide proper exposure forthe subject range.

Where ambient (steady state) illumination is negligible, the timedinterval and the flash firing time (following first light through theshutter) will be equal; however, ambient light can be accounted for inthe present invention by triggering the flash after a period dependenton both the ambient light and subject range.

In one of the illustrated embodiments, a sonic rangefinder is utilizedfor initiating an integrator circuit after an interval of time,subsequent to transmission of a sonic burst, to provide a flash firetime linearly proportional to the range of the subject returning theecho. The integrator includes a resistor in parallel with a photocellexposed to light from the scene, and a trigger circuit responsive to theoutput of the integrator for firing the flash and closing the shutterwhen the output reaches a predetermined trigger level. Preferably, theshutter opening (i.e., first light) is delayed, after transmission ofthe sonic burst, by a predetermined period of time which is the sametime as the integrator would require for its output to reach the triggerlevel when the ambient light on the photocell is negligible. As aconsequence, under very low ambient light level, essentially only theresistor is effective in the integrator and the flash is triggered andshutter closed a fixed time subsequent to detection of an echo; thefixed time being equal to the delay time in opening the shutter. Whenambient light is present, it contributes to the integrator summing toreduce the flash fire time in accordance with the ambient level and thescan rate such that the firing of the flash and closing of the shutteroccurs sooner, i.e., at a smaller aperture, than would be the case werethe integrator time-out determined solely by the resistor. Consequently,the flash is fired before the exposure aperture area has reached itsoptimum size with respect to the range of the subject thereby reducingthe amount of light transmitted by the shutter from the subject due toits flash illumination; this reduction in flash illumination beingbalanced by the ambient light present such that a proper exposure isobtained.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are disclosed in the accompanyingdrawings wherein:

FIG. 1 is a composite plot showing the variation in brightness of asubject due to flash illumination as a function of distance of thesubject to a camera, and the variation in exposure aperture area as afunction of time resulting from the parametric relationship betweensubject brightness and time arising from the functional relationshipbetween subject distance and time;

FIG. 2 is a block diagram showing a first embodiment of the inventionideally suited for taking photographs under flash illumination whenambient scene light is negligible;

FIG. 3 is a time diagram showing the variation of the exposure aperturearea of the scanning shutter shown in FIG. 2;

FIG. 4 is a block diagram of the preferred embodiment of the inventionfor photographing an object illuminated by both flash and ambient light;

FIG. 5 is a series of plots showing the time relationship betweenactuation of the shutter and the firing of the flash when ambient scenelight is negligible;

FIG. 6 is a plot similar to FIG. 5 but showing the situation whenambient light is present in the photographic scene under exposure; and

FIG. 7 illustrates an alternate embodiment of the system of FIG. 4 anddepicts an arrangement for providing a flash fire interval as anon-linear function of subject range.

DETAILED DESCRIPTION

The present invention is based on utilizing a scanning shutter whoseprogram, i.e, time-wise variation in exposure aperture area, is selectedsuch that if A is the instantaneous area of the aperture when the flashor, that is, transient illumination occurs, and if B is the brightnessof the subject due to its illumination by the flash, then A×B is aconstant which in independent of range. This implies that the amount oftransient scene light incident on the photographic film operativelyassociated with the shutter will always be the same. With a given filmspeed and light output of the flash, proper exposure of the film will beassured independently of subject range up to a maximum range determinedby the maximum size of the exposure aperture area and the flash output,assuming ambient scene light is negligible.

Prior to describing the illustrated embodiments in detail, it should benoted that the term "flash" is intended to include any transient lightpulse and while the invention is preferably practiced with an electronicflash or strobe whose pulse duration is quite short as compared to theshutter scan time, it is also applicable to longer duration lightpulses, such as from incandescent flash units.

The manner in which a program for a scanning shutter can be selected isillustrated in FIG. 1, wherein the scales have been chosen to fit thecurves onto the space available and are of no significance to thepresent invention. Reference numeral 10 is a curve that shows thevariation in brightness of a subject, due to its illumination by a flashof given output, as a function of subject range from the flash source,or from the camera where the flash is relatively close thereto. Curve 10demonstrates the inverse square relationship between subject brightnessand range, i.e., B f(1/d²). If time intervals are considered asrepresentative of subject range, i.e., t f(d), then both the brightnessof the subject and the time intervals are functions of the parameter"distance". Consequently, the brightness of the subject due to itsillumination by flash is a parametric function of time.

If the time interval representing subject range is a linear function ofdistance as indicated by curve 12, then curve 14 represents theparametric relationship of subject brightness with time. Obviously,curve 14 does not infer that the brightness of a subject illuminated byflash changes with time, but merely shows that if the range of a subjectis d₀, whereby its brightness is B₀, then if the flash is fired at timet₀ corresponding to the distance d₀, the brightness of the subject willbe B₀ as indicated in FIG. 1. Since the relationship between range andtime is assumed linear as indicated by curve 12, the direct relationshipbetween time and the brightness of the subject due to the flashillumination will vary as the inverse square of this time as shown bycurve 14.

In accordance with the invention, it follows that for the presentembodiment, curve 16, which represents the timewise variation inexposure aperture area of the scanning shutter, is inversely related tocurve 14. That is, curve 16 varies with the square of time forembodiments where the range related time parameter is linear with range.

Conventional techniques are available for designing the shapes ofexposure apertures in superposed flat blades that constitute a diaphragmor scanning shutter in order for the shutter aperture area or aperturevalues to have a time-squared program. However, according to the presentinvention, the exposure aperture area of the scanning shutter can haveprograms other than the one shown by curve 16 and, in fact, can belinear or have an arbitrary time variation dependent only on the natureof the range-time function. For example, it may be desirable to have alinear scan program rather than a time-squared scan program either formechanical or design reasons, or in order to retrofit an existingscanning shutter camera with the present invention. Curve 18 representssuch a linear program for the scanning shutter; and it requires thebrightness curve 20 to have a 1/t form in order for the product of areaand brightness to remain constant. The nature of curves 10 and 20 aresuch that the range-time variation must satisfy the relationship t f(d²)as indicated by curve 22.

The desired relationship between range and time can be established byutilizing a member having a physical property whose value isrepresentative of the range of a subject. For example, for a linearrange factor the member can be a resistor in an integrator because thevale of the resistance in a simple integrator is linearly related to thetime required for the integrator output to reach a predetermined value.A linear potentiometer whose setting is responsive to the setting of anoptical rangefinder is a practical way to establish time as a functionof range. As another example, the round trip time for a sonic burst totravel between a transmitter and subject is linearly related to therange of the subject. Similarly, for different scanning programs, anon-linear relationship between range and time can be established bysuitable modifications of the systems described above.

While the below-described embodiments are illustrative of moveable lenscameras which first employ subject ranging to position the lens, this isquite separate from range firing of the flash and the latter may beemployed with a fixed lens or, that is, fixed focus cameras.

Referring now to FIG. 2, reference numeral 24 designates a cameraincorporating a first embodiment of the invention utilizing a scanningshutter 26 having a t² program as indicated by curve 27 in FIG. 3, and alinear range-time relationship by reason of an integrator 28. A firstmanual input 29 to a range finder 30 is utilized for the purpose ofadjusting a linear potentiometer 32 of the integrator to a valuedirectly proportional to the range of an object 33 from the camera 24.Rangefinder 30 can be a conventional optical rangefinder wherein theuser views the object and mechanically moves an arm 34 until the objectis in proper focus. In such case, the setting of the potentiometer 32would be responsive to the movement of arm 34. In addition, the arm 34may move a lens mount or lens assembly 36 until the lens assembly is ina position at which light from the object 33 will be focused on aphotosensitive sheet of film 38 after the shutter 26 is achieved by asecond manual input 39 which also closes a switch 40 thereby coupling apower source such as a battery 42 to the integrator 28.

As shown in FIG. 3, the second manual input 39 occurs subsequent tocompletion of the focus; and it is assumed that first-light through thescanning shutter is substantially coincident with the initiation of theintegrator 28. The voltage at node 44, which constitutes the output ofthe integrator, changes exponentially with time and reaches a triggerlevel which is sensed by a Schmitt trigger 46 after a period of timedirectly proportional to the range of object 34 from the camera. Thetrigger 46 responds, when the voltage at node 44 reaches thepredetermined trigger level, by sending a firing signal to a flash unit48 which is preferably, but not necessarily, an electronic flash whoseduration is very much shorter than the duration of the scanning time asshown in FIG. 3. Consequently, in this embodiment, the firing of theflash 48 occurs, following first light, after an interval of time whichis directly proportional to the range of the object.

For the reasons indicated above in connection with the discussion ofFIG. 1, the area of the exposure aperture of the shutter 26 will have afunctional relationship to the transient brightness of the object withthe result that the amount of light passing through the scanning shutterand incident on the film 38 will provide proper exposure, assuming thatambient light is negligible and that the object 34 is within the maximumrange of the system as determined by the maximum exposure aperture area.Assuming substantially all of the light incident on the film 38 isderived from the flash 48 (i.e., the ambient light is negligible), theshutter may be closed at any time following completion of the flashpulse.

The timing of the flash in accordance with subject range during shutterscanning synchronizes the flash with a narrow range of apertures inaccordance with subject distance, and for an electronic flash,effectively synchronizes the short pulse of illumination withessentially a fixed aperture; that is in the latter case, any change inaperture during the extremely short flash pulse can often be consideredto have minimal effect on the expected exposure.

Rangefinders other than optical rangefinders can be utilized inconnection with the apparatus shown in FIG. 2 and, preferably,rangefinder 30 is in the form of a sonic rangefinder of the typedisclosed in copending application Ser. No. 840,802, filed Nov. 11,1977. In such case, the time required for a sonic burst to pass from atransducer (not shown) to the object and back to the transducer is afunction of the range of the object. Consequently, the receipt of anecho can be utilized for the firing of flash 48 and the integrator 28may be essentially eliminated. That is, for a fixed focus camera, theshutter actuation (first light) and the transmit pulse are synchronized,the shutter scans at a time squared program, and the echo triggers theSchmitt trigger to fire the strobe pulse at the appropriate aperturevalue.

The above description of FIG. 2 is based on the assumption that ambientlight is negligible such that it provides an insignificant contributionto the exposure of the film 38. In order to account for ambient light,the arrangement shown in FIG. 4 can be utilized wherein camera 24'utilizes a sonic rangefinder in conjunction with a delayed opening ofthe shutter so that flash fire time predicted by the sonic range timemay be reduced to account for ambient light.

Rangefinder 30' shown in FIG. 4 is a schematic illustration of therangefinder disclosed in the above-noted application Ser. No. 840,802wherein it is employed for focusing a movable lens arrangement. Whilesuch lens focusing arrangement may be utilized in the presentembodiment, it is not necessary to the description of the presentinvention, and hence, details thereto are omitted for clarity. A manualinput indicated at 50 will automatically focus the lens assembly 36consistent with the range of the object 34 as indicated and also actuatethe scanning shutter 26 after a predetermined time delay δ provided by adelay circuit schematically indicated by block 52. The manual input 50to rangefinder 30' causes a ranging circuit 54 to issue a transmitcommand to sonic transducer 56 causing a burst of sonic energy 58 to beemitted from the transducer substantially coincident with manual input50. An echo detector 66 which detects echo 62 after processing by theranging circuit, closes a switch arrangement 40' associated with anintegrator 28'. When the switch 40' closes, the voltage at the outputnode 44, of integrator 28', begins to increase exponentially inaccordance with the value of capacitor 70 and the effective value of theresistance of the integrator which comprises the parallel combination ofa fixed resistor 72 and a photodiode 74 located behind the photocellapertures of the scanning shutter and exposed to light from the scenebeing photographed when first light passes the exposure apertures of theshutter. When the voltage at node 44 reaches the trigger level, Schmitttrigger 46 fires flash 48 and terminates the scanning operation of theshutter by closing the same.

The manner in which the apparatus shown in FIG. 4 will achieve properexposure over a wide range of ambient lighting conditions is set forthin FIGS. 5 and 6. To simplify the explanation, the flash is presumed tobe an electronic flash which conventionally provides a pulse ofrelatively short duration. FIG. 5 relates to the condition in whichambient light is negligible as described above in connection with FIGS.2 and 3. In FIG. 5(a), the possible variation in aperture area of thescanning shutter as a function of time is shown by curve 76. In camera24', as described with regard to FIG. 4, the shutter is actuated so thatfirst light occurs after a time interval δ following manual input 50.Recalling that this time interval is equal to or longer than the timerequired for an echo to return from an object located at the maximumflash range of the camera, FIG. 5(a) shows that receipt of echo 62occurs within the interval δ, and follows the manual input by a periodof time functionally related to the range of the object. Thus, switch40' (FIG. 4) is closed prior to first light through the scanning shutterwith the result that battery 42 is applied to integrator 28' coincidentwith recept of echo 62. However, since the ambient light is negligible,the resistance of photodiode 74 will be high and the effectiveresistance of the integrator circuit is essentially the resistance ofthe resistor 72 which is selected such that the trigger level at node 44is reached after a time interval δ'. Consequently, the "delayed echo" orthe output of the Schmitt trigger 46 occurs after a period of time ε'following echo 62 as shown in FIG. 5(a). Consequently, the flash 48 isfired and the close command applied to the shutter 26 in response totriggering of the trigger 46 which is subsequent to first light throughthe shutter by a period of time equal to the period of time betweenreceipt of the echo 62 and the instant of manual input 50. That is, inthis instance, the flash fire time as measured from camera actuation isequal to the sum of the range related time plus the shutter delay δ. Thesolid portion 75 of curve 76 represents the change in area from firstlight to receipt of the closing command; while curve 77 represents thechange in area as the shutter responds to the closing command.

Referring now to FIG. 5(b), the voltage at node 44 is shown asincreasing from zero at the instant of receipt of echo 62 towards thebattery voltage and reaching the trigger level 78 after a period of timeδ' equal to the delay time δ described above. Upon reaching the triggerlevel 78, the Schmitt trigger 46 fires flash 48 and closes the shutter.At that time, photodiode 74 responds to the impulse-like light output offlash 48 by a sudden decrease in resistance to a level related tosubject range producing the step-like increase 80 in the voltage at node44; however, since the Schmitt trigger has already been tripped, thelatter is of no consequence.

The amount of light incident on the film 38 operatively associated withthe scanning shutter 26 is shown in FIG. 5(c). During the time intervalδ', no light is incident on the film since it has been assumed that theambient light is negligible. When the Schmitt trigger 46 detects thetrigger level at node 44 and fires the flash, the light incident on thefilm will increase to level 79 dependent upon the product of thebrightness of the object due to its illumination by the flash pulse andthe area of the shutter at substantially the instant the flash is fired,assuming, of course, that the flash fire and flash pulse aresubstantially simultaneous and that the light pulse is very short, asnormally produced by electronic strobes. By proper selection of theparameters of film speed, light output of the flash, and the design ofthe scanning shutter, a proper exposure of the film can be obtainedindependently of subject range. Note that the finite closing time of theshutter does not affect the amount of light incident on the film becausesubstantially all of the light came from the very short duration flash.

In the event that the ambient scene light is not negligible, thephotodiode 74 will contribute to the film exposure and shorten the timeat which the flash is fired in accordance with the level of ambientlight. As shown in FIG. 6(a), detection of echo 62 by the detector 66causes the integrator 28' to be initiated prior to first light and thevoltage at node 44 (FIG. 4) initially begins to change exponentiallytoward the battery voltage 42 in the same manner as shown in FIG. 5(b).At a time δ following manual input 50 when first light occurs withrespect to the film operatively positioned behind shutter 26, firstlight also occurs with respect to photodiode 74. The ambient lightreduces the resistance of the photodiode, and hence, the time constantof integrator 28', in accordance with the amount of ambient lightresulting in the break, shown at 82 in FIG. 6(b), in the summing rate ofthe output of the integrator. Consequently, the output begins toincrease more rapidly toward the battery voltage and reaches triggerlevel 78 in a time shorter than δ , depending on the level of ambientlight. Hence, the time period selected for the flash firing inaccordance with subject distance is reduced in accordance with theambient light. Double-ended arrow 86 indicates the time-wise positionsof step 84 which are dependent on both subject range and the ambientlevel.

When the flash is fired (by the trigger 46) the resistance of thephotodiode 74 is significantly reduced as in the previous case whereambient light is negligible, and a step-like increase 84 occurs in thevoltage at the output node 44' of the integrator. In this arrangement,since the close command or termination signal is applied to the shutterby the trigger at the same time as the flash is fired, the contributionof the ambient light to the exposure is essentially that occuring priorto the flash.

The amount of light incident on the film 38 as a consequence of ambientlight and the flash illumination of the subject is shown in FIG. 6(c).During the time interval between receipt of the echo and first light, nolight from the scene being photographed is incident on the film. Betweenfirst light and until the flash is fired, ambient light enters theexposure aperture, with this amount increasing with the increase in theexposure aperture value. Prior to firing the flash, the integrated lightwill be at a level 88 depending, of course, on the intensity of theambient scene light. Then, when the trigger 46 detects the predeterminedvoltage level at node 44, it fires the flash such that the lightincident on the film increases rapidly. However, since the area of theexposure aperture at the instant the flash is fired is smaller than itwould have been if firing of the flash occurred at time δ (as in FIG.6c) the flash contribution to the exposure has been reduced to accountfor ambient light. Consequently, the exposure, due to both the flash andto the ambient light prior to the flash, reaches the level 90 andbecause of the finite closing time of the shutter, ambient lightcontinues to contribute slightly to film exposure after the short flashpulse as indicated by segment 92 in FIG. 6(c). By the time the shutteris completely closed, the exposure light will have reached level 79,which as previously indicated, is sufficient to properly expose thefilm.

For clarity of the description, the shutter actuation delay δ and theflash fire delay δ' were considered equal; however, this assumes thatshutter actuation and first light are simultaneous, hence in practicethe flash fire delay will be slightly greater than the shutter actuationdelay by an amount equal to the difference between shutter actuation andfirst light.

In FIG. 7, the flash fire circuit of FIG. 4 is modified to provide aflash fire interval which is a non-linear function of the subject rangefor use with a shutter scan rate having other than a time squaredprogram. In this figure, the resistor 72 is replaced by a diode 96 whichprovides a flash fire time interval as a logarithmic function of thesubject range for use with a linear shutter scan rate.

Additionally, the flash fire time interval may be varied to suitdifferent scan rates by adding a plurality of diodes (not shown) withappropriate series resistors to produce any desired functionalrelationship between the subject distance and the flash fire timeinterval. Consequently, the embodiment of FIG. 4 illustrates a systemhaving means (e.g., sonic) for defining a time interval functionallyrelated (e.g., linearly) to subject distance and means (switch 44' anddiode 96) for converting the above time interval to a flash fireinterval non-linearly related to subject distance to accommodate aselected shutter scanning function.

It is believed that the advantages and improved results furnished by theapparatus of the present invention are apparent from the foregoingdescription of the several embodiments of the invention. Various changesand modifications may be made without departing from the spirit andscope of the invention as sought to be defined in the claims thatfollow.

What is claimed is: .[.
 1. Apparatus for photographing a subject,comprising:a scanning shutter which when actuated produces apredetermined, timewise variation in exposure apperture area; rangingmeans for providing an output representative of the range of a subject;a flash unit; and means for actuating the shutter to start its scanning,the improvement comprising: means for firing the flash unit to produce aflash of illumination after a time period, measured from the first lightthrough the shutter, dependent on the output of the ranging means, therelationship between the time period and subject range establishing aparametric relationship between the brightness of the subject due to itsflash illumination and the scanning time of the shutter, the inverse ofthis parametric relationship constituting the timewise variation in theexposure aperture area of the shutter..].
 2. Apparatus .[.according toclaim 1.]. .Iadd.for photographing a subject, comprising:a scanningshutter which when actuated produces a predetermined, timewise variationin exposure aperture area; ranging means for providing an outputrepresentative of the range of a subject; a flash unit; .Iaddend.and.Iadd. means for actuating the shutter to start its scanning, theimprovement comprising: means for firing the flash unit to produce aflash of illumination after a time period, measured from the first lightthrough the shutter, dependent on the output of the ranging means, therelationship between the time period and subject range establishing aparametric relationship between the brightness of the subject due to itsflash illumination and the scanning time of the shutter, the inverse ofthis parametric relationship constituting the timewise variation in theexposure aperture area of the shutter; and .Iaddend. wherein saidrelationship between said time .[.interval.]. .Iadd.period .Iaddend.andrange is linear, and the exposure aperture area varies as the square ofthe timing during scanning. .[.
 3. Apparatus according to claim 1wherein the ranging means includes an integrator whose output isrepresentative of the range of the subject and which begins to integratein response to actuation of the scanning shutter, and wherein the meansfor firing the flash unit includes a trigger circuit that fires theflash unit when the output of said integrator reaches a predeterminedtrigger level..]. .[.4. Apparatus according to claim 3 wherein saidintegrator has a resistor whose value is directly related to the rangeof the subject..]. .[.5. Apparatus according to claim 4 wherein thevalue of said resistor is set in accordance with the range of thesubject..].
 6. Apparatus .[.according to claim 3 wherein.]. .Iadd.forphotographing a subject, comprising:a scanning shutter which whenactuated produces a predetermined, timewise variation in exposureapperture area; ranging means for providing an output representative ofthe range of a subject; a flash unit; and means for actuating theshutter to start its scanning, the improvement comprising: means forfiring the flash unit to produce a flash of illumination after a timeperiod, measured from the first light through the shutter, dependent onthe output of the ranging means, the relationship between the timeperiod and subject range establishing a parametric relationship betweenthe brightness of the subject due to its flash illumination and thescanning time of the shutter, the inverse of this parametricrelationship constituting the timewise variation in the exposureaperture area of the shutter; the ranging means includes an integratorwhose output is representative of the range of the subject and whichbegins to integrate in response to actuation of the scanning shutter;the means for firing the flash unit includes a trigger circuit thatfires the flash unit when the output of said integrator reaches apredetermined trigger level; and .Iaddend.the range means includes aphotodetector responsive to light from the subject for modifying theoutput of the integrator in accordance with ambient light.
 7. Apparatus.[.according to claim 1 including.]. .Iadd.for photographing a subject,comprising: .Iaddend.manually operable means .[.,.]..Iadd.; a scanningshutter which when activated produces a predetermined, timewisevariation in exposure apperture area; ranging means for providing anoutput representative of the range of a subject; a flash unit; and meansfor actuating the shutter to start its scanning, the improvementcomprising: means for firing the flash unit to produce a flash ofillumination after a time period, measured from the first light throughthe shutter, dependent on the output of the ranging means, therelationship between the time period and subject range establishing aparametric relationship between the brightness of the subject due to itsflash illumination and the scanning time of the shutter, the inverse ofthis parametric relationship constituting the timewise variation in theexposure aperture area of the shutter, and .Iaddend. the means foractuating the shutter being responsive to operation of said manuallyoperable means for actuating the shutter to produce first lighttherethrough after a first predetermined time delay, and wherein saidranging means includes an integrator circuit having an electricalelement in parallel with a photodetector exposed to light from thesubject, and a trigger circuit responsive to the output of theintegrator for firing the flash and closing the shutter when theintegrator output reaches a predetermined trigger level, said integratorcircuit being energized, subsequent to operation of said manuallyoperable means, after a period of time related to the range of thesubject, and said electrical element of said integrator having a valuesuch that the output of said integrator will reach said predeterminedtrigger level in a second time delay equal to said first time delay suchthat, when the ambient light on the photodetector is negligible, saidflash is fired after a time equal to the sum of said first predeterminedtime delay and said range related time .[.interval.]..Iadd.period.Iaddend..
 8. Apparatus according to claim 7 wherein therange means includes a sonic rangefinder which transmits a burst inresponse to operation of the manually operable means, and whichprocesses an echo from the subject such that receipt of the echoinitiates said integrator circuit.
 9. A method for recording the imageof a subject illuminated at least in part by actuation of a flash unitto produce a pulse of transient illumination and employing a scanningshutter arrangement actuable to initiate an exposure interval duringwhich said shutter arrangement at least initially provides progressivelyincreasing aperture values through which scene light from said subjectis transmitted to a photosensitive recording medium, said methodcomprising the steps of:determining the distance between said subjectand said flash unit and defining a time interval related to saiddistance; driving said shutter arrangement at a scanning rate selectedin accordance with said relationship between subject distance and time;and actuating said flash unit to produce said pulse of illuminationfollowing said actuation of said shutter after a time period related tosaid time interval so that said pulse is automatically synchronized witha narrow range of aperture values selected in accordance with subjectdistance. The method of claim 9 including the steps of determining theambient light in the scene and reducing said time period proportionatelythereto so that said pulse of illumination is synchronized with a secondnarrow range of aperture values of smaller value than thefirst-mentioned range.
 1. The method of claim 9 wherein said determiningand defining step includes defining a range related time intervalmeasured from a given starting time, driving said shutter such thatfirst light thereof occurs after a time delay of a longer time asmeasured from said starting time than that anticipated for said rangerelated interval, and actuating said flash unit after a time period asmeasured from said starting point not greater than the sum of said rangerelated time interval and said time delay.
 12. The method of claim 11including determining the ambient light level in the scene and reducingsaid time period in accordance therewith to define a second time period,and actuating said flash unit after a third time period, as measuredfrom said starting point, equal to the sum of said second time periodand said time delay.
 13. In a flash exposure control system forrecording scene images of a subject to produce a proper exposure of aphotosensitive recording medium independent of subject distance, saidsystem having a scanning shutter arrangement actuatable for at leastinitially providing increasing aperture values during an exposureinterval within which scene light is transmitted to the photosensitiverecording medium, said shutter arrangement providing said increasingaperture values at a predetermined scanning rate such that, followingactuation of said shutter arrangement, progressively increasing aperturevalues are provided at progressively increasing time intervals followingsaid actuation, means for producing a flash of illumination during saidexposure interval to illuminate said subject with transientillumination, means for determining the distance of said subject fromsaid flash producing means and for synchronizing the production of saidflash with operation of said scanning shutter arrangement so thattransient illumination reflected from said subject is transmittedthrough said shutter arrangement to said recording medium by a narrowrange of aperture values selected in accordance with subject distance,the improvement wherein said distance determining and flashsynchronizing means comprises means for defining a range related timeinterval corresponding to subject distance and for producing said flashof illumination responsive to a lapse of a time period measured fromfirst light of said shutter arrangement and proportional to said rangerelated time interval to thereby produce said flash over a narrow rangeof aperture values automatically selected in accordance with subjectdistance.
 14. The improvement of claim 13 wherein said distancedetermining and flash synchronizing means includes a range finder whichdirectly produces said range related time interval defined by theelapsed time between transmission of a burst of energy toward thesubject and return of an echo of energy therefrom.
 15. The improvementof claim 13 wherein said scanning rate is selected to provide aperturevalues increasing as the square with time, said range related timeinterval is linearly related to subject distance and said time period isdirectly proportional to said range related interval.
 16. Theimprovement of claim 13 wherein said scanning rate is selected toprovide aperture values increasing linearly with time and said timeperiod is proportional to the square of the subject distance.
 17. Theimprovement of claim 13 wherein said distance determining and flashsynchronizing means includes a sonic ranging system for producing arange related time interval linearly related to subject distance. 18.The improvement of claim 13 wherein said distance determining andsynchronizing means additionally includes means for evaluating theambient light level in said scene and for reducing said time period inaccordance with ambient scene light.
 19. The improvement of claim 13additionally including means for actuating said distance determining andsynchronizing means and for then actuating said shutter to produce firstlight therethrough after a selected delay, and wherein said distancedetermining and synchronizing means includes means for actuating saidflash producing means after an elapsed time, measured from said systemactuation, comprised of the sum of said delay and said time periodproportional to said range related interval.
 20. The improvement ofclaim 19 wherein said distance determining and synchronizing meansincludes a delay circuit for producing a second time periodsubstantially equal to said selected delay and for actuating said flashproducing means at the end of said second period, and means foractuating said delay circuit at the end of said range related timeinterval whereby said flash fire time is substantially the sum of saidselected delay and said range related time interval.
 21. The improvementof claim 20 additionally including means for reducing said second timeperiod in accordance with the level of ambient scene light.
 22. Theimprovement of claim 20 wherein said distance determining andsynchronizing means includes a voltage sensitive trigger circuit foractuating said flash producing means when said trigger circuit reaches agiven voltage level, said trigger circuit including a voltage summingelement fed by both said delay circuit and a light sensitive networksuch that the actuation of said flash producing means is a function ofboth said subject distance and said ambient scene light level.
 3. Theimprovement of claim 22 wherein said distance determining andsynchronizing means includes a trigger circuit for producing a flashfire signal to actuate said flash producing means, said trigger circuitincluding a voltage summing element fed by both a timing network and alight sensing network such that the voltage of said summing element isresponsive to both networks, and said timing network provides a timingfunction related to said subject distance.
 24. A method for recordingthe image of a subject illuminated at least in part by actuation of aflash unit to produce a pulse of transient illumination and employing ascanning shutter arrangement actuatable to initiate an exposure intervalduring which said shutter arrangement at least initially providesprogressively increasing aperture values through which scene light fromsaid subject is transmitted to a photosensitive recording medium, saidmethod comprising the steps of:transmitting a burst of energy towardsaid subject and receiving an echo therefrom so as to define a timeinterval related to subject distance; driving said shutter arrangementat a scanning rate selected in accordance with the relationship betweensubject distance and time; and actuating said flash unit upon receipt ofsaid echo to produce said pulse of illumination, following saidactuation of said shutter, after a time period related to said timeinterval so that said pulse is automatically synchronized with a narrowrange of aperture values selected in accordance with subject distance.